The invention concerns valves, especially those designed for use in controlling flow of heating and cooling fluids in various heating, air conditioning and ventilation systems. The invention provides inexpensive valves of the curtain valve type that can operate at very low torque and have the ability to be adjusted to a range of flow coefficients. Thus, fewer valves must be maintained in inventory to meet demand for a full range of valve sizes. The valves can have a variety of utilities in a wide range of sizes, but are especially useful as zone valves, enabling operation by a simple and inexpensive actuator. In the preferred forms, the valves exhibit a long life span and can be easily replaced or repaired as needed.
There are currently a variety of on-off zone control valves that have the advantage of being relatively inexpensive, making them useful for commercial as well as residential applications. Unfortunately, these valves as presently available suffer from a number of limitations due to their structures which affect the ability to open, close off or perform other control functions at high flow coefficients and differential pressures. As generally available, these valves are not capable of operating with a constant, low close-off torque independent of flow coefficient. Moreover, they each have a predetermined fixed flow coefficient (degrees of opening), which cannot be easily adjusted.
Exemplary of the type of valves and associated actuators in wide use and in need of lower cost alternatives, are those shown in U.S. Pat. No. 6,073,907, and the prior art cited therein. As commonly available, on-off zone control valves control flow of hot or chilled water to terminals and are usually in the sizes of ½″, ¾″, 1″ and 1 ¼″. Each size is made in a variety of flow coefficients (Cv). They are available as two-way or three-way valves and are typically operated by on-off thermostats. Power-to-close and power-to-open valves exist. Currently, large inventories are required to meet the full range of flow rates.
A zone control valve of the type shown in U.S. Pat. No. 6,073,907, typically has an essentially cylindrical cavity with circular cross section and two openings for fluid flow in and out of the cavity. In this regard, reference can be made to FIG. 4 of U.S. Pat. No. 6,073,907. The valves have an arm with a closure, e.g., a disk or flapper, mounted on one end. The arm and closure pivot on a shaft rotatable about an axis so that the closure can be moved to cover and uncover an opening by moving over and away from the opening, thereby permitting or stopping the flow. The direction of the flow is from an inlet opening into the cavity and out of the cavity past the closure through an outlet opening. The torque required is first to compress the disk enough for close-off, and then to provide a force sufficient to overcome the force produced by the differential pressure working over the area of the opening. Operating in this manner, fluid pressure strives to open the valve.
A drive mechanism, typically including a cogwheel segment located outside the valve body, rotates the shaft about the axis. The drive can be spring loaded to bias the closure in one way or the other, depending upon if it is a power-to-open or power-to-close valve. The valve, or actuator, is typically capable of operating at pressures of from about 10 psi up to a maximum of about 60 psi. The lower number is valid for high flow coefficients.
The cogwheel segment is driven by a small gear, which in turn is connected to a gearbox and a small AC motor. In a power-to-close valve, the motor runs in one direction only when power is applied and stalls when the mechanism has closed the valve. When power is not applied, the biasing spring causes the motor and gearbox to run backward and open the valve.
One drawback of this prior art design is that low close-off pressures are not satisfactory for the larger flow coefficients. Another, is that the drive mechanism has a limited life span due especially to wear of the cogwheel segment and gear.
Valves having flexible curtain closure members for providing adjustable flow control are available for large-scale installations, but have not been thought suitable for low-cost, HVAC applications. Curtain valves tend to leak at low pressures and tend to be large and to require costly hand assembly in a manner making them unsuitable for use in HVAC and related systems.
It remains that valves currently available for use in HVAC applications have a number of failings in terms of effective operation, high cost, and the need to inventory a large number of sizes. And, as currently available, curtain valves cannot be made economically for HVAC or other systems requiring relatively small sizes.